1. Field of the Invention
This invention relates to a polarized electromagnetic apparatus in which a movable core assembly is driven by the combined attracting force of a permanent magnet and a electromagnetic coil, and more specifically to the construction of the movable core assembly.
2. Description of the Prior Art
FIGS. 4A and 4B show the construction of a conventional polarized electromagnetic apparatus disclosed, for example, in the Japanese Patent Unexamined Publication No. 79304/1988. FIG. 4A represents the movable core assembly in a reset state and FIG. 4B in an attracted state. The arrow indicates the flow of magnetic flux. In the figures, reference numeral 1 denotes a U-shaped stationary core and 2 and L-shaped pole plate. Designated 4 is a movable core spindle which has a first movable core plate 5 and a second movable core plate 5a, both secured to the end surfaces thereof to form a movable core assembly.
Designated 6 is an electromagnetic coil and 7 a permanent magnet. One of the pole faces of the permanent magnet 7 is placed in contact with the central portion of the U-shaped stationary core 1 and the other pole face is placed in contact with the central portion of the L-shaped pole plate 2.
P represents a first magnetic gap formed between the leg of the U-shaped stationary core 1 and the first movable core plate 5. Q indicates a second magnetic gap formed between the first movable core plate 5 and the leg of the L-shaped pole plate 2. R1 is a third magnetic gap formed between the second movable core plate 5a and the other leg of the U-shaped stationary core 1.
The above is the construction of the conventional polarized electromagnetic apparatus. When the electromagnetic coil 6 is not energized, the greatest attractive force generated by the flux of the permanent magnet 7 indicated by broken line arrows in FIG. 4A acts upon the first magnetic gap P. The movable core assembly therefore is forced in the Y direction and attracted to the leg of the U-shaped stationary core 1, so that it is maintained in the reset condition.
When under this condition the electromagnetic coil 6 is energized, magnetic flux indicated by solid line arrows in FIG. 4A is generated. In the first magnetic gap P, the flux (broken line arrows) of the permanent magnet 7 and the flux (solid line arrows) of the electromagnetic coil 6 cancel each other, reducing the attractive force. In the second and third magnetic gaps Q, R1, the combined attractive force is produced by the permanent magnet 7 and the electromagnetic coil 6. The combined attractive force acting on the second and third gaps Q, R1 is greater than the attractive force in the first gap P, driving the movable core assembly toward the X direction until it comes in contact with the other leg of the U-shaped stationary core 1. The movable core assembly is now kept in its attracted state by the flux indicated by the solid line arrows and the broken line arrows in FIG. 4B.
Let us take a contactor for example. Though not shown, the contactor has a trip spring and a spring for generating the contact pressure, all these spring loads acting in the Y direction as a reactionary force. Under the attracted state, when the electromagnetic coil 6 is deenergized, the movable core assembly is driven in the Y direction to return to the reset state because the reactionary force is set larger than the attractive force of the flux generated by the permanent magnet 7.
In such a conventional polarized electromagnetic apparatus where the movable core assembly has the first movable core plate 5 and the second movable core plate 5a secured to each end surface of the movable core spindle 4, the complete movable core assembly cannot be installed into the electromagnetic coil 6. Thus, it is necessary to first pass the movable core spindle 4 through the electromagnetic coil 6 and then fix the first movable core plate 5 or the second movable core plate 5a to the movable core spindle 4. This makes the assembly work difficult.